1. Field of the Invention
The present invention generally relates to semiconductor devices and, more particularly, to a semiconductor device having a three-dimensional structure in which a plurality of semiconductor devices and semiconductor elements are stacked, and a manufacturing method of such a semiconductor device.
With the development of electric equipments in recent years, a demand for miniaturization in dimensions and thickness, multifunction, high-performance and high-density in the semiconductor devices has been increasing. In order to cope with such a demand, the structure of the semiconductor devices has been shifting to a three-dimensional structure in which a plurality of semiconductor devices or a plurality of semiconductor elements are stacked.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 2001-223297 discloses an example of a semiconductor device, which has a three-dimensional structure formed by stacking a plurality of semiconductor devices. FIG. 1 is a cross-sectional view of the semiconductor device disclosed in the above-mentioned patent document.
In FIG. 1, semiconductor chips 3 are mounted on both sides of each of interposers 1, and are encapsulated by a seal resin 2, respectively. The two interposers 1 are stacked with the seal resin 2, which encapsulates the semiconductor chip 3, interposed therebetween. The interposers 1 are connected to each other by bonding solder balls 7 to ball pads 5 which are exposed in through holes 6 formed in a solder resist 4. That is, the upper and lower interposers 1 are electrically connected to each other by the solder balls 7, and are also connect mechanically to each other.
In the semiconductor device shown in FIG. 1, since each semiconductor chip mounted on the stacked interposers is encapsulated by the seal resin, it is necessary to provide a distance between two interposers, which distance is greater than the thickness of the seal resin layer interposed between two interposers. Therefore, if the distance between the interposers can be reduced, the overall height of the semiconductor device can also be reduced.
Additionally, since the interposers are connected and fixed to each other by the solder balls provided in the peripheral portion of the interposers, if a warp occurs in the interposers in a stacking process of an assembling process of the semiconductor package, a defect may occur in the connecting part between the interposers. Moreover, when mounting the complete semiconductor package onto a substrate, a defect may occur in the connecting part between the interposers due to a thermal deformation of the interposers and remelting of the solder balls.
Furthermore, since the complete semiconductor package is mechanically connected by a small area with only the solder balls, a stress tends to be concentrated into the connecting part between the interposers, which may deteriorate mechanical reliability of the package.
It is a general object of the present invention to provide an improved and useful semiconductor device in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a semiconductor device having a three-dimensional structure in which a plurality of semiconductor devices or a plurality of semiconductor elements are stacked, the semiconductor device having a reduced overall height and an improved reliability in the mechanical strength of the stacked structure.
Another object of the present invention is to provide a semiconductor device having a three-dimensional structure in which a plurality of semiconductor devices or a plurality of semiconductor elements are stacked, the semiconductor device having an improved heat release characteristic.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a semiconductor device comprising: a first semiconductor element having a circuit forming surface and a back surface opposite to the circuit forming surface; a first interposer having a surface on which first electrode pads are formed and the first semiconductor element is mounted with the circuit forming surface facing the first interposer; a second semiconductor element having a circuit forming surface and a back surface opposite to the circuit forming surface; a second interposer having a surface on which second electrode pads are formed and the second semiconductor element is mounted with the circuit forming surface facing the second interposer, the second electrode pads for connection with the first interposer; and external connection terminals provided on a surface of the second interposer opposite to the surface on which the second semiconductor element is mounted, wherein the first interposer and the second interposer are electrically connected to each other by conductive members between the first and second electrode pads, and the back surface of the first semiconductor element and the back surface of the second semiconductor element are fixed to each other by an adhesive.
According to the above-mentioned invention, there is no need to encapsulate the first and second semiconductor elements provided between the first and second interposers. Thus, a distance between the first and second interposers can be reduced, which results in a reduction in an overall thickness of the semiconductor device. Additionally, since the first and second semiconductor elements are bonded to each other by the adhesive, a mechanical strength of the connection between the interposers is improved, which prevents warp of the interposers. Further, since the first and second semiconductor elements are bonded to each other by the adhesive, a heat generated in the first semiconductor element can be efficiently released outside through the second semiconductor element and the second interposer.
The semiconductor device according to the present invention may further comprise at least one third semiconductor element which is mounted on a surface of the first interposer opposite to the surface on which the first semiconductor element is mounted. Accordingly, the number of semiconductor elements stacked in the semiconductor device can be increased, which improves a packaging density. Additionally, a plurality of the third semiconductor elements may be mounted and encapsulated on the surface of the first interposer in a stacked and fixed state. Accordingly, semiconductor elements of different kinds or sizes can be efficiently arranged within the semiconductor device. Further, a metal layer for heat release may be provided on a surface of the first interposer opposite to the surface on which the first semiconductor element is mounted. Accordingly, the metal layer serves as a heat spreader, which can efficiently release a heat of the semiconductor elements to outside of the semiconductor device.
Additionally, there is provided according to another aspect of the present invention a semiconductor device comprising: a first semiconductor element having a circuit forming surface and a back surface opposite to the circuit forming surface; a first interposer having a surface on which first electrode pads are formed and the first semiconductor element is mounted with the circuit forming surface facing the first interposer; a second semiconductor element having a circuit forming surface and a back surface opposite to the circuit forming surface; a second interposer having a surface on which second electrode pads are formed and the second semiconductor element is mounted with the circuit forming surface facing the second interposer, the second electrode pads for connection with the first interposer; and external connection terminals provided on a surface of the second interposer opposite to the surface on which the second semiconductor element is mounted, wherein the first interposer and the second interposer are electrically connected to each other by conductive members between the first and second electrode pads, and the first interposer and the back surface of the second semiconductor element are fixed to each other by an adhesive.
According to the above-mentioned invention, there is no need to encapsulate the second semiconductor element provided between the first and second interposers. Thus, a distance between the first and second interposers can be reduced, which results in a reduction in an overall thickness of the semiconductor device. Additionally, since the second semiconductor element and the first interposer are bonded to each other by the adhesive, a mechanical strength of the connection between the interposers is improved, which prevents warp of the interposers. Further, since the second semiconductor element is bonded to the first interposer by the adhesive, a heat generated in the first semiconductor element can be efficiently released outside through the first interposer, the second semiconductor element and the second interposer.
The semiconductor device according to the present invention may further comprise at least one third semiconductor element mounted on the surface of the first interposer on which the first semiconductor element is mounted. Accordingly, the number of semiconductor elements stacked in the semiconductor device can be increased, which improves a packaging density. Additionally, the semiconductor device may further comprise at least one third semiconductor element is stacked on the first semiconductor element, and the first and third semiconductor elements may be encapsulated on the first interposer.
Additionally, in the semiconductor device according to the present invention, at least one fourth semiconductor element may be mounted on the surface of the second interposer provided with the external connection terminals. A plurality of the fourth semiconductor elements may be provided and encapsulated on the second interposer.
Further, each of the external connection terminals may be a flat pad, or may have a protruding shape. Each of the external connection terminals may be a lead terminal extending in a direction outward from the second interposer.
Additionally, the adhesive, which bonds the back surface of the first semiconductor element and the back surface of the second semiconductor element to each other, may be a thermosetting type resin adhesive. The thermosetting type resin adhesive may contain at least one of silver and copper.
Further, in the semiconductor device according to the present invention, a reinforcing adhesive may be provided to connecting parts between the conductive materials and the first and second interposers. The reinforcing adhesive may be made of an insulating thermosetting type resin material. The reinforcing adhesive may be in the form of a film having openings corresponding to positions of the conductive members.
Additionally, there is provided according to another aspect of the present invention a manufacturing method of a semiconductor device comprising a first semiconductor element and a second semiconductor element, comprising the steps of: mounting the first semiconductor element onto a first interposer in a state in which a circuit forming surface of the first semiconductor element faces the first interposer; mounting the second semiconductor element onto a second interposer in a state in which a circuit forming surface of the second semiconductor element faces the second interposer; electrically connecting the first interposer and the second interposer to each other by stacking the first and second interposers with the second semiconductor element interposed therebetween and heating conductive members provided between the first and second interposers so as to melt the conductive members; and curing a thermosetting adhesive provided between a back surface of the second semiconductor device and one of a back surface of the first semiconductor element and the first interposer by a heat in the step of electrically connecting.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.